Single filament yarns of this type are disclosed in International Patent Application WO 90/14453. The maximum modulus of the polyketone yarns described in said document generally is satisfactory. Also, some yarns of satisfactory tenacity are described. However, the elongation at break of yarns which possess such satisfactory tenacity is low, as a result of which the yarns are not always suitable for application in industry. The yarns described in this application which do have sufficient elongation at break are substantially less strong, so that, generally speaking, it can be argued that the overall quality of the yarns according to this document is found insufficient for every practical application.
Yarns of the type mentioned in the opening paragraph are also disclosed in EP-A-456 306. In this document, a yarn of good overall quality is described. However, the yarn is obtained by spinning through 6 capillaries, which means that the yarn is comprised of 6 filaments spun simultaneously. Such a slender yarn is not suitable for industrial practice.